Process of manufacturing shaped bodies from iron powders



Patented Feb. 29, 1944 rnocnss or MANUFACTURING snsrnn BODIES FROM IRONrownnas Claus Guenter Goetzel, Yonkers, N. Y., assignor to :AmericanElectro Metal Corporation, Yonkers, N. Y., a. corporation of Maryland NoDrawing. Application November 8, 1940,

Serial No. 364,814

3 Claims.

This invention relates to the production or shaped sintered iron bodiesof the character of steel or alloy steel, from powdery initial material.

Heretofore it was dimcult or impossible to produce by sinteringsteel-like articles shaped ready for use, of desirable density, carboncontent, as well as mechanical properties from powdery initial material.

Powdery sponge iron could be compacted under pressures amounting to fromto tons per sq. inch into briquets and sintered, however, this sort ofiron is impure, relatively expensive, and

not always available, and the sintered bodies are very soft and porousor deformed.

Electrolytic iron of highest purity can be compacted into shaped bodiesat pressuresamounting to about 50 to 60 tons per sq. inch and sintered;it is howeverve y expensive and the sintered bodies are extremely soft,porous or deformed. Powders of commercial cast iron containing about 2%to 4.5% carbon, cannot be commei-cially and satisfactorily compacted atall, even if pressures up tolOO tons were applied previous to sintering:slip faces are apt to develop during pressing which render the materialuselessfor m st purp s s- ,Bythaadmlxtureof pure iron powder to porousbody results upon. sintering -'which does not exhibit the character ofsteel.

Ordinary kinds of steel powders when pressed up to even 200 tons per sq.inch result in fragile compacts, developing slip faces and beingpractically useless for further manipulation and treatment. 1 A

I It has been suggested therefore to produce iron powder ofpredetermined carbon content (steel powder) by desoxidizing andthereafter carburizing finely divided iron oxide, and subsequentlydecarburizing those not yet briquettable particles in superficial layersso as to obtain individual grains consisting of a core comprising ironand combined carbon and a case or shell of substantially pure iron. Thepure iron case or shells render the particles briquettable underpressure;

briquettable. This process also is difllcult as to the control of theuniform carbon content of the articles, and thelatter cannot becompacted easily. By annealing'a pearlite, or pearlite-cementite, orpearlite-ferrite structure is imparted to the particles depending upontheir carbon con- "tent, and their ability 'of being welded together ina'sintering process without simultaneous application of high pressure ispoor.

It has also been suggested to carburizeiron powder, to dilute it withpure iron powder-and upon sintering, however, more or less densecommolded to desired shaped compacts, and were annea ed so as to rendethem relatively so t a d thereby to enhance the compressibility of themix, press the mixture to shape, sinter the shape within austenitictemperature range and to con tinue that heating until the carbidecomprised bythe carburized iron is uniformly diffused through the mass.Instead of carburized iron, steel powder could be used. Thismethodobviously requires a long extended heating at relatively hightemperatures and is therefore rather uneconomical.

It is therefore an object of the invention to produce shaped sinteredbodies of the character of steel, in a less expensive and more efllcientway .-.than heretofore. It'is, another object of the invention to use ina compacting and sintering process normally (1. e.,

the cast iron powder, a under commercially practicable pressures)'nonbriquettable powders of steel; as available in the market withoutsubstantially ail'ecting and particularly changing the carbon content ofthose powders before compacting them.

It is a particular object of the invention to produce dense and shapedsintered bodies from different kinds-of iron powders, one of which issubstantially ferritic, while the other or others 'atleastone other kindforms a carbon to below 1.7% containing iron alloy which is normally notbriquettable,the heterogeneous and dense body so obtained having adesired average carbon c0ntent and offering desirable mechanical" and/orthermal and heat treating qualities, such as to, tensile strength anddeformation and/or malleability.

It is a further object ofthe invention to produce by commerciallypracticable pressures and sintering, shaped bodies from two or morekinds of iron powder; one of which is substantially pure iron or Ierrtic in characte whi e at e st ne ther iorms steel or an alloy thereof,which is lormally not briquettable, and to consolidate hem into aheterogeneous body or desired aver- .ge carbon content,'desired densityand mechanial and/or thermal properties' 1 It is possible to manufacturesubstantially pure nd soft iron powder or ferrite by desoxidizing atlevated temperatures finely divided iron oxide in he presence of adesoxidizing medium, such as nely divided lampblack' or hydrogen, carbonionoxide gas, gaseous hydrocarbons, and in parlcular methane or naturalgas.

It is obviousthat ferritic iron powder obtained 1 this or any other way,such as from pure elec- 'olytic lron, or particularly from reducedsponge on, is plastic, malleable and ductile, and that its articles arecapable of beingkwelded together wen in the cold under suitable andcommercially racticable pressure. I

Ferritic iron powder is used according to the lventi'on in amounts fromabout 5% to 70% but referably only up'to 40% to 60%. as a binder for;her iron powders containing combined carbon id/or other admixtures, iidesired, as used in lloyed steels and which are, at leasfih part, nor-.ally not briquettable. I iromium, cobalt, nickel, tantalum, vanadium,licon, titanium, manganese and phosphorus ay be mentioned by way ofexample as such imixtures.

In particular, the ferritic iron powder is used I a binder in admixturesto other powders of eel or alloyed steel, in order to render briquettaethe mixture containing those normally nonriquettable powders.

Steel powder is available in the market as ushed steel, either inparticle sizes suited for re purpose of the invention, or sieved inorder I separate from coarser particles the finer ones lapted for theinvention. If'no powder of steel desired description is available or iffor other asons manufacture of the steel powder is prerred, this can bedone in well known manner heating scrap sheets, shot or ingots of steelto )Ollt 700 to 900 C, and above (but below meltg temperature),quenching and thereafter ushing the brittle-steel'to desired particlesize:

ushing and sieving may be repeatedly applied itil desired small particlesizes are obtained. Jose powders are normally not briquettable. Theinvention is however not limited to'the e of steel powder. Powders ofalloy steel such containing molybdenum, tungsten, tantalum, nadium,silicon, phosphorus, manganese, nickel, romium and/or cobalt,furthermore of stainless eel, nicrom, etc., may be used, in order tointro- :ce desired admixtures into the final body. If r reasons to bedescribed hereinafter, ratios of use admixtures are desired which arenot prestin steel or iron alloys available in th market, e alloys may beprepared in a well known manr, the molten alloy solidified by quenchingand ereafter crushed and preferably sieved. in preparing an initialmixture of the binder .d up to 1.7% combined carbon and, if desired, neradmixtures containing iron powder, in genll the following difl'erentways can be taken. r simplicitys sake, only ferritic iron powder d steelpowder are referred to in the following scription, but it should beunderstood that in- :ad of steel powder, powders of alloy steel alloy ingeneral, powders of iron containing up to combined carbon and any otherdesired adxture, and powdery mixtures, can be used. It ould also beunderstood that instead of one kind of steel powder, diflerent kinds ofsteel powders, particularly steel and alloy steel powders, or ingeneral, two or more different kinds of iron powders containing up to1.7% combined carbon and other desired admixtures may be used at leastone of which is normally not briquettable.

First, fine ferritic iron andv equally fine steel powder may be admixed;this can be done for any kind of powders and purposes. Second,relativeabout .8 C).

coarse steel powder may be admixed; therebythe:

Tungsten, molybdenum,

ly coarse ferritic iron powder and fine steel powder may be admixed;this is of certainadvantage for low carbon steel powders (containing upto Third, fine ferritic iron powder and ferritic powder can beeasilysmeared around the steel particles during mixing in ball mills in thecold or heat which is particularly advantageous ii. relatively largeamounts (up to'about of binder are used. Fourth, coarse ferritic ironpowdel; and equally coarse steel powder may be admixed." j

While for the purpose of this description 01' the invention powders ofa'particle size corresponding up to about 100 mesh may be convenientlycalled coarse powders, those of particle sizes correspondritic binderand steel powder in the mixture play an important part'in the selection.The larger the amount of binder, the coarser the particles can be.Third, although a heterogeneous product is eventually obtained, theaverage carbon content of the sintered body depends upon the ratio inwhich ferritic and particularly pure iron powders are admixed with otherkinds of iron powder, containing combined carbon. The average amount oi!other additions, such as mentioned above, present in the completedsintered body also depends upon that ratio. In the latter respect it isto be observed that during the sintering process and particularlydepending upon its duration, a more or less complete diflusion of carbonfrom the combined carbon containing powder particles into the i'erriticparticles occurs, as shall be described more in detail later on, and inthe same way other admixtures, such as mentioned above, difluse more orless from the iron or steel alloy particles into the ferritic ones.

Thus the ultimate properties, structure and composition of the sinteredand cooledabody greatly depend upon the initial mixture andthe ratiosand particle sizes of the diirerent'kin'ds of powders admixed. I

In general, according to the invention, the ferritic iron or binder maybe used in amounts from about 5% to balance substantially iron powder orpowders containing up to 1.7% combined carbon and/or other admixtures01' the type referred to above.

The difierent kinds of iron powder thus chosen are to be intimatelymixed, and whatever the size of the powder particles may be, mixing inball mills, particularly using steel balls and steel linings, has provedadvantageous. Mixing may be performed at room or elevated temperatures.

Mixing in ball mills may either be carried out in dry or wet mills. Inthe latter case, carbon tetrachloride, acetone, benzine, etc. may beused ticular preparation of the powders.

fect any. of the 4 types of mixtures referred to ritic particles under'pressure, whereby the chas proper wetting agents. Also water inwhich up to about. 1% lamp black orgraphite is suspended, may be' used.Inthis case the temperature should be room temperature and in any 7event below the evaporation temperature of the 1? wetting agent.Whenever wet milling is applied, the intimate mixture eventuallyobtained is to be dried andprecautions must be taken against oxidation.

The mixture prepared as described above in general is ready for pressingunder commercially practicable pressures, e. g., 10 to 50 tons p. s. i.into acoheren't compact of desired shape. However, it;is sometimesdesirable to interpose apar- To this efabove, but preferablyconsistingof fine ferrite 1 and coarser steel powders of about .3 to .8C content, is filled into a boat of steel or other suitable material andpushedthrough a furnace of the continuous operation type. in which atemherence of the pressed body is assisted.

- Due to thepresence of binder of ferrltic, soft and malleableiron,'.the'compacting can be performed under commercially practicablepressures "pretreated to obtain sherardizing eflects in the peraturepreferably up to 500 to 600 C. and an inert or reducing atmosphere ismaintained. The

1 latter may be produced by the use of desiccated hydrogen, carbonmonoxide, natural gas, nitrogen, cracked gases, etc. The heat treatmentmay be applied for a considerable period of time, from about 20 minutesto one hour or longer. In place of a stationary furnace, a rotaryfurnace may be used in which additional mixing on even ball milling ofthe powders-is combined with the intended heat treatment.

The preliminary heat treatment just described results in someboundarydiilusion. between the particles of ferrite and mosecr ne otherpowder or powders, or a'sherardi'sation of the latter. It should beobserved, however, that by this heat treatment, if applied, thestructure and particularly the composition of the individual particlesshould not be changed materially and: only, in general, the combinedcarbon containing steel particles provided with a mechanically adheringfilm of more ferritic character.

The thus preliminarily treated mixture may be pressed immediately orfurther comminuted in a dry ball mill.

The above preliminary treatmentis particularly advantageousifrelatively. small amounts offerrit c binder are used, such as from 5%to 15%.

In such cases, but also in the presence of higher amounts of ferriticbinder it has been foundthat the pressures to ,be applied forcompactingcan be considerably reduced, or the period of presintering orsintering at, highest temperature somewhat shortened. l v

The mixture prepared in any way described above is now subjected tocompacting into coherent bodies of desired shape in molds.

A particular object of the invention consists in manufacturing shapedproducts of steel or alloy steel character containing between .1% to1.5% combined carbon, by sintering from an initialmixture of suitablepowders. der is substantially spongy andrelatively plastic. Steel powderobtained from eutectoid steel contains about 0.9% carbon andis either ofpearlitic' or martensitic structure. Steel powder obtained fromhypereutectic steel is either martensitic or pearlitic and cementitic ina structure, while powder obtained from hypoeutectoid steel -is eithermartensitic or psarlitic and ferritic.

The powder particles obtained from any such brittle steel are sharp,angular and extremely hard and therefore apt'to interlock with and to .1

pierce into t e w p y and malleable Ferritic iron pow-v way describedabove,pressures from 3 to 15 tons per sq.'inch suiflce, the lower valuespertaining to to binderwand the higher values to about 20% to 30%ferritic binder'present. In order'to facilitate the shaping andcompacting at very low pressures, it is sometimes desirable to admix abinder, such a 'dextrine, glucose, or

a 'polyvalent-alcohol, such as glycerine, in small amounts ofabout 1% to2% by weight of the entire mixture. Such binderevaporates or burns ofiattlow temperatures during presintering' or wheniinal sintering isstarted, and such evap-- oration does not result in porosity of thefinal body. If an organic binder is used and carbonized, it adds to thecarbon content of the mixture which i to be taken into considerationwhenthe 'final carbon content of the body is calculated. The pressurealso depends on the particle. size and loading weight ofxthe powder; andthe finer and lighter particularly the powders of binding material are,the lower may be the pressure. In the pressedand coherent body'thusobtained the particles of all the powders used in the initial intimatemixture are uniformly distributed.

Though the body is still porous, the particles are brought into intimatecontact and the shapes of the soft ferritic powder particles are closelyadaptedgto those of and interlocked with the harder combined ironcontaining particles. Thereby effective -'sintering within periods asshort as possible is considerably assisted. The

j coherence of-the pressedbodies sufllces fortaking them out of themolds and subjecting them to sintering. Dueito the presence of the softferritic binder which also acts like a lubricant, the wear of the;diesduring pressing and by the pressed bodies is minimized.

The shaped pressed bodies are either immediately subjected to high andfinal sintering, or

r first to presintering. It is well known in the art that'presinteringtemperature is about 20% to 30% below the melting pointofthe mixture, and

if presintering is desired. the pressed bodies are subjected to suchtemperatures (between about,

sintering in an inert or reducing atmosphere,

such as desiccated hydrogen, etc. Y If carbon containing gases areused,such as natural gas, hydrocarbons,,generator gas, etc.,

they are to be diluted by other gases,'such as hydrogen, ifslight'additional carburizationof the body under treatment is toice-avoided.

A presintering step is desirable in somecases .for well known reasons,particularly in order to remove oxidefilms from particles and todegasify .the body and to shortenthe final sintering period. T epresintered body may be pressed again in ejecting, A

the cold or heat, and/or shaped additionally, e. g., by machining. fl

The pressed, and if desired, presintered bodies are then subjected tofinal sintering. The temperatures of final sintering depend considerablyupon the character of the mixture. It is well known in the art that themelting point of iron depends upon the amount of combined carbon, andother admixtures alloyed therewith. While pure iron melts at about 1550C., its melting temperaturedecreases to about 1150 C. with increasingcarbon content up to 4.2%; with further increased carbon content themelting temperature slowly increases again, but iron with such highcarbon content is of no practical interest forthe present inventionwhich is confined to the manufacture of shaped iron bodies containingabout .1% to 1.5% C. Within the lower part of this range, up to about35% C, the invention is particularly suited for the manufacture of morecomplicated shapes, such as those having undercuts, or whenever greataccurateness is required, such as for gears and tools,

while ordinary steel with a carbon content of and those notrequiringmachining for accurateness after casting. In the range above 1.5%carbon, malleable cast iron which contains above 2% carbon can be used,and the invention does not pretend to compete with such malleable castllOIl.

It is well known that final or high sintering temperatures lie ingeneral about below the melting point of a metal or mixture of metalscapable of sintering, and thus it is easily possible to calculate orestablish by analysis the average carbon content of the entire mixtureof iron powders, then to establish from well known ironcarbon diagramsthe melting temperature of iron with that carbon content, and tocalculate therefrom the final sintering temperature to be expected; thelatter can easily be verified by a few experiments.

The same holds true for mixtures containing, besides ferritic iron andsteel, also other admixtures such as mentioned above. The ranges ofmelting temperatures of those iron or steel alloys are well known, andby calculating from the ratios of the individual melting temperatures ofdifierent kinds of powders, the approximateaverage melting temperatureof the mixture, and from the latter the final sintering temperature tobe expected, a basis is found for eventually establishing the actualfinal sintering temperature of the mixture by a few-experiments.

Thus in general the final sintering of powder mixtures according to theinvention will be accompli ed within a temperature range from about 1150C. .to about l390 C.v It should be observed, however, that the highestsintering temperature of any powder is by no means as fixed a value asthe melting temperature, but actually covers a range above and below thetheoretical value; it should, however, always be considerably below atemperature at which the entire mixture or any part of it melts.

Th period of sintering depends to some degree upon the size or thepowdery particles; the finer the particles the shorter that period. Italso depends upon the size of the article to be made since the heatpenetrates faster through a small article than through a larger one.With this understanding, the average period of sintering should be givenwith about 10 minutesto one hour.

It is to be understood that the carbon content of the steel powder willdefine the average carbon content of the sintered product. Assuming amixture consisting of 25% or powdery ferritic binder and powdery steelof 0.8% carbon content, the average carbon content of the final bodywill amount to .6% carbon, provided no carbon is burned oil? by anoxygen containing atmosphere and sintering is consequently performedeither in an atmosphere inert or neutral to carbon, or in vacuo.

If a higher average carbon content of the final mixture is desired,particles of steel of' higher carbon content, up to about 1.5% should beused.

It is evident that in such a case also two or more kinds or steelpowders may be admixed; one

of the lower carbon content, c. g., .8% carbon, the

other of the higher carbon content, e. g., 1.5% carbon, and the ratiosof the ferritic iron, as well as of the two kinds of steel powders areto be calculated so as to result in the desired average content ofcarbon.

Any suitable furnace can be used for sintering,

such as push furnaces of the continuous operation type as describedabove for desoxidizing purposes, and in particular resistance orinduction (high frequency) furnaces. Any protective, in particular inertor reducing or even carburizing atmosphere may be used during sintering,or a vacuum applied. Sintering may also be performed under pressure, ifdesired in more exceptional cases. As to the operation of the highsintering process, the following should be understood although theinventor does not intend to confine himself to any theory of hisinvention.

During high sintering at temperatures of or exceeding 1150 C., not onlycompacting and agglomerating of the powdery particles occurs, as is thecase in ordinary sintering processes like in the production of hardmetals which contain carbide particles bonded by iron group metal, or inother composite bodies of the structure of agglomerates.

While in ordinary sintering processes aiming at mere agglomeration, abinder of lower melting point than the other components of the mixtureis used and becomes highly plastic or even melts while the othercomponents remain substantially solid, it should be observed that theferritic binder used by the invention is mostly of the highestmeltingpoint of all components of the mixture. However, according to theinvention the ferrite is used as a convenient binder for compacting themixture preferably in the cold under commercially practicable pressures,and during final sintering the binder and the combined carbon containingcomponents obviously exchange their roles; those components becomehighly plastic first, cause shrinking of the mass and closest contactbetween them and the .ferritic particles as well as most probablywetting of the latter, thereby diifuslon of carbon into the intimatelycontacting ferritic particles and lowering of their sinteringtemperature is accomplished gradually, resulting eventually in asubstantially equal sintering temperature of all particles present inthe mixture and their com plete sinter.

However, if the desired final sintering temperature is considerablylower than about 1300 C. and if a relatively large amount of ferrlticbinder is present, it is somet mes advisab e t heat the mixture at thestart of sintering at least to about 1300 C. and to gradually reducethat starting to the desired final sintering temperature after about 5to 20 minutes have passed and some diffusion of carbon into the ferritehas occurred. At 1300 0., steel even of 1.7% carbon content will bestill solid though highly plastic.

In general, and if the articles are not too large, during the periodwhile the mixture is heated up to sintering temperature suflicientdiffusion of carbon into the ferritic particles will occur, wherebytheir sintering temperature is lowered and that the steel particlesisraised (because their content of combined carbon is correspondinglyreduced), and sintering. can be performed throughout at the desiredfinal temperature without using the temperature regulation describedabove.

Thus, by properly choosing the ratio of carbon present in the mixture tothe entire iron amount of the latter, and controlling the temperatureand period of sintering, the mass gradually adopts the character ofaustenite, if the total amount of carbon compared to the total amount ofiron present in the mass does not exceed about 1.5%. At hightemperatures exceeding about 1360' C., the maximum limit of carbonallowing formation of austenite gradually decreases.

Upon slowly cooling the mass from sintering temperature to roomtemperature, upon passing the temperature corresponding to thetransformation point As, the mass if austenitic in character andcontaining about .9% carbon, converts itself into pearlite while ahigher carbon content results in pearlite plus cementite and a lowercarbon content into pearlite plus ferrite. If'due, e. g., to controlledfinal sintering at lower temperature or for a shorter period thannecessary to cause carbon to diffuse into all ofthe ferritic binder, apart of the latter remained virgin, the cooled product consists of aphase of that virgin ferrite, and other phases resulting from theremaining mass which'at -sintering temperature either was austenitic oraustenite plus cementite.

The structures of these other phases depend on the carbon content ofthat remaining mass; if the latter contained .9% carbon, pearliteresults, while with a higher carbon content pearlite plus cementite andwith a lower carbon content pearlite plus additional ferrite (which maybe conveniently called secondary ferrite) results.

If a mass of any of the types referred to is subjected to controlledparticular quenching, martensite results.

From this it follows that from a process according to theinvention,.upon controlled sintering and cooling in general, a. materialof the shaped body greatly resembling or equalling ordinary steelresults.

If for one reason or the other, controlled sin tering to this effectcannot be performed in"a single step, and a true steel is desired, theshaped body can be pressed again preferably in the heat and attemperatures close to but below its melting temperature in molds of ashape and size taking into account any shrinkage during the firstsintering. Pressing by exerting a heavy stroke is preferred. The thuspressed body is then sintered for a second time, and these operationsrepeated,

if necessary, until the desired structure or density is obtained.

From the above it also appears that by con by sufficiently extendedsintering in general pearlprocess applied according to the invention formanufacturing the desired shaped bodies is substantially the same asdescribed. The phenomenae occurring during controlled sintering dependhowever on the capability of the admixture to diffuse from the steelalloy into the ferrite particles. While cobalt, nickel and molybdenumdifi'use quite easily, manganese and chromium diffuse slowly and to alimited extent, particularly if they are present in relatively largeratios in the added alloy. Thus, the final shaped body will be of al-10y steel character, and the admixtures will either be uniformlydistributed throughout, or be present only or mainly in particles orcrystals-resulting from the originally admixed alloy steel particles.However, the finer the original powders are, and the more thorough thesinter, the more the distribution of difilcultly difiusing admixtureswill resemble a uniform distribution, and the body will exhibitproperties almost completely resembling those of alloyed steel.

It is evident from the foregoing that the ratio of admixtures of thetype referred to in'the final body will depend upon its total amountintroduced by the steel or iron alloy in proportion not available on themarket, particular alloys trolled sintering and cooling according to theinvention the final structure of a mass of given composition can bedefinitely determined. While or prealloys of iron and the desiredadmixture should be prepared and added to the initial-mixture insuitable amount. Such alloys are also available in the market, andferromanganese, ferromolybdenum, ferronickel, ferrosilicon,ferrotitanium, ferrovan'adium, stainless steel (scrap), ferrochrome andferrotungsten can be used for this purpose. The admixture may be added,however, also in powdered virgin state and not alloyed with iron, etc.to the initial mixtures. Y

The shaped body obtained according to the invention can be subjected toany further treatment. If it is finished ina desired shape, ready foruse, it might be case hardened or "hardened by annealing andquenching,or normalized, or softened and somewhat more homogenized by annealingonly; If the body is, e. g., in the shape of a rod orv ingot, it might'be subjected to mechanical'trea'tment such asslicv scribe the qualityof a temperature or period of sintering, as well as I the manner coolingthe body. Thus grain growth. and recrystallisation can size, or crystalbe well controlled. Care should be taken that the carbon content ismaintained and that decarbuiization beavoided by the 'use'of properprotecting atmospheres at temperatures where decarburization mightotherwise occur.

If for. any reason, such as for the purpose of saving on relativelyexpensive desiccated hydrogen, some decarburization should occur duringsintering, it can be taken care of by admix-- ing to the initialmixturesteel particles or highor carbon content or in larger relative amountwhich, upon being partly decarburized still yield the desired averagecarbon content or the final iron mass. To the same effect, solid carbonsuch as lamp black may be admixed to the initial powder before pressing.

Ii 10: any other reasoncarburization occurs during sintering, forinstance because natural gas (methane) is available at low cost, thisshould be taken care 01 by dosing the carbon containing components ofthe mixture, so that upon carburization during sintering, the desiredaverage content of carbon of the iron mass results.

For some molding purposes a certain minimum loading weight of theinitial powder is desired. The loading weight of powdery sponge iron. ismostly about-.15v gr./cc., and. that of steel powder 3 to-3.5 g'r.--/cc.By proper dosing the ferrite. and steel. components according to theinvention, desired loading weights of the initial mixture can beobtained, Thus 40% to 60% of ferritic "iron powder (1-50 mesh) of 1.5loading weight, have been admixed with a balance of steel'powder (150mesh) containing 0.7% C and. having a loading weight of 3.5; theresulting mixtureshada loading weight of 2.4 to

2.6 which is' demanded for many large scale briquetting (and sintering)purposes.

In the appended claims the term normally not briquettable" or similartermsare to depowder not toiorm coherent bodiesof desired shapes capableof being further manipulated, upon. cold molding under normal pressures,i. e., up to about 50 tons p. s. i.

It should be understood that the invention. is not limited to anyexemplification herein described, butis to be derived in its broadestas- .pect from the appended claims.

WhatI claimis: 15in a method of producing from powdery I material. bycompacting under pressure and sintering shaped bodies substantially ofthe character ofsteel or alloy steel and essentially free or graphite,the steps of intimately admixing powder. selectedffrom the groupconsisting of steel and alloy steel powders, at least a substantial partof said powder always containing" combined carbon in an amount from .1%

to below 1.7% and being normally not briquettable, with about 5% toabout 70% ferritic iron powder, shaping and compacting the mixture underpressure, and heat treating the shaped compact under controlledconditions until a predetermined amount of said carbon diflused intosaid ferritic iron and a dense body of predetermined composition. ofsteel or alloy steel is obtained, said conditions including finalsintering at controlled temperatures close to but below the prevailinglowest melting temperature of any of said powders and final body withinthe temperature range or 1150 to about 1390 C. and application of aselected atmosphere.

2. In a method of producing from powdery material by compacting underpressure and sintering shaped bodies substantially of the character ofsteel or alloy steel and essentially tree of graphite, the steps ofintimately admixing at elevated temperatures up to about 600 C.

powder selected from the group consisting of steel and alloy steelpowders, at least a substantial part of said powder always containingcombined carbon in an amount from .1% to below 1.7% andbeing normallynot briquettable, with about 5%toabout 70% ferritic iron powder,

' shaping and compacting the mixture under pressure, and heat treatingthe shaped compact under controlled conditions until a predeterminedamount o! l said carbon diflused into said ferritic iron, and a densebody substantially of the composition of steel or alloy steel and ofpredetermined average content of combined carbon within the range of .l%to 1.5% carbon is obtained,.said conditions including final sinteringclose to but below the prevailing" lowest melting temperature of any ofsaid powders and final about 1390 C. and application of a selectedatbody within the temperature range of 1150 to about 1390" C. andapplication of a selected atmosphere.

3. In a method of producing from powdery material by compacting underpressure and sintering shaped bodies substantially of the character ofsteel or alloy steel and essentially free of graphite. the steps ofintimately admixing powder selected from the group consisting of steeland alloy steel powders, at least a substantial part of .said powderalways containing combined carbon in an amount from .1% to below 1.7%and being normally not briquettable, with about 5% to about 70% ferriticiron powder, shaping and compacting the mixture under pressure,presintering said shaped compact at temperatures from about 750 to below1050 C. in a selected atmosphere, and heat treating the shaped compactunder controlled conditions until a dense body substantially of thecomposition of steel or alloy steel and of predetermined average contentof said combined carbon within a range from .1% to 1.5% carbon isobtained and a predetermined amount of said carbon diffused into saidierritic iron, said conditions including final sintering close to butbe- 7 low the prevailing lowest melting temperature of any of saidpowders and final body'within the temperature range of 1150 to about1390 C. and application of a selected atmosphere.

CLAUS 'GUENI'ER GOETZEL.

